This invention relates to a toroidal continuously variable transmission.
Tokkai Hei 7-198014 published by the Japanese Patent Office in 1995 and Tokkai Hei 11-159590 published by the Japanese Patent Office in 1999, disclose a toroidal continuously variable transmission. Tokkai Hei 11-159590 describes a power roller supporting mechanism which can pivot. On the other hand, Tokkai Hei 7-198014 describes a power roller supporting mechanism which does not use an eccentric shaft.
However, there was the following problem in the prior art power roller supporting mechanism.
In the structure described in Tokkai Hei 11-159590, an eccentric axis is supported so that it can rotate relative to a trunnion, and a rotation axis on the trunnion side and the rotation axis on the power roller side of the eccentric shaft are offset. This offset is used as a power roller gyration mechanism. The offset amount is equivalent to a pivot arm length. Due to this gyration mechanism, the number of component parts is large, and cost is high.
A gap is formed between the eccentric shaft and the trunnion, and between the eccentric shaft and a inner wheel of the power roller. As a result of this gap, due to the fluctuation of a force in a tangential direction received by the power roller inner wheel from the input/output disks, a position of the power roller relative to the trunnion in a gyration axis direction varies, and a torque shift therefore occurs. At this time, an outer wheel of the power roller engages with the eccentric shaft, so displacement of the eccentric shaft is suppressed. The eccentric shaft inclines relative to the gyration axis, however as the power roller outer wheel is pushed against the trunnion by a thrust force due to the power roller inner wheel, it remains parallel to the gyration axis. Therefore, due to the inclination of the eccentric shaft, when the eccentric shaft engages with a hole on the power roller outer wheel, it engages while center lines are offset relative to each other, and there is a risk that an edges of an engaging hole will deform or wear down.
This deformation or wear causes a time-dependent variation in the ease with which the eccentric shaft inclines, i.e., a time-dependent variation in torque shift characteristics. This time-dependent variation is undesirable from a viewpoint of speed ratio control of the vehicle.
If the power roller outer wheel is made to fit loosely with the eccentric shaft to prevent this time-dependent variation (if the gap is set large), a torque shift amount increases which is also undesirable for speed ratio control of the vehicle.
Torque shift is a phenomenon wherein a real speed ratio varies from a target speed ratio determined based on vehicle running conditions according to an input torque.
In the structure described in Tokkai Hei 7-198014, a needle bearing is interposed between the power roller housing of the trunnion and the power roller outer wheel, and this is used as a slide mechanism of the power roller inner wheel. Therefore, the number of component parts is large and cost increases due to the use of this slide mechanism.
It is therefore an object of this invention to provide a toroidal continuously variable transmission having a power roller supporting structure which maintains a required power roller slide function or gyration function, and eliminates the problem of rigidity inherent in transmissions without an eccentric shaft or torque shift problems inherent in transmissions with an eccentric shaft, by a simple structure with a small number of component parts.
In order to achieve above object, this invention provides a toroidal continuously variable transmission comprising: an input disk and an output disk disposed facing each other on a common axis, power rollers provided so that it can transmit power between these input/output disks, press member disposed at a rear of one of the input disk and output disk which presses in the direction of the other disk, and trunnions which support the power roller free to rotate and is able to gyrate around a gyration axis perpendicular to a rotation axis of the power roller, wherein the trunnions support the power rollers , so that they support a thrust force acting in the power rollers rotation axis direction and a traction force acting in the gyration axis direction ,the each of power rollers comprise a power roller inner wheel in frictional contact with the input/output disks, a power roller outer wheel supported in the trunnion, a ball bearing interposed between the power roller inner wheel and the power roller outer wheel , and an inner wheel supporting shaft which supports the power roller inner wheel such that it is free to rotate, the shaft having a shaft base part provided in the trunnion , and arranged so that the radial support rigidity is set high in the gyration axis direction and set low in the direction perpendicular to the trunnion gyration axis and the power roller rotation axis, and when one of the disks is pressed and displaced in the direction of the other disk by a press member , the power roller inner wheel displaces with the ball bearing by the displacement of the one of the disks.